1. Field of the Invention
The present invention relates to a method of controlling an idling wind turbine in particular comprising a sensor system and a control system, and comprising the steps of measuring, comparing, computing and correcting the pitch angle of a wind turbine.
2. Description of Related Art
The present invention further relates to wind turbine with a sensor system comprising at least one sensor with a wind sensor configured to measure/detect wind condition data in the vicinity and preferably up-wind of the wind turbine and a control system comprising at least one computer with means for executing a control algorithm and configured to process sensor input from the sensor and to compute an optimal pitch angle value that results in a minimal mechanical load of least one rotor blade on the hub when the wind turbine is not producing power.
In wind turbine, design constraints are often fatigue loads or extreme loads.
This is true for rotor blades, the hub, the main frame, the mains shaft etc. Furthermore, the foundation is most often designed to extreme load constraints.
Focus has been on reducing the fatigue loads or to improve the fatigue properties of the materials used for the components or structures.
A person skilled in the art, who wants to build larger wind turbines or operate wind turbines, including larger wind turbines, in extreme areas or environments—including those areas with regular or frequent typhoons or hurricanes—will be inclined to reinforce the components or structures.
Such standard approaches by the person skilled in the state of the art will however not lead to a durable wind turbine in such extreme environments.
It is noted that extreme conditions do depend on the size of the rotor size. In general a larger rotor will imply the introduction of extreme conditions at lower wind speeds that for smaller rotors.
WO 2011/124230 A2 discloses a control method of a wind turbine with multiple flaps and strain gages arranged on each rotor blade for altering the aerodynamic performance of the blade. A controller located in the nacelle determines an optimal pitch angle for each rotor blade based on the measured wind speed, the yaw error and the azimuth angle for reducing the extreme loads on the blade. The flaps and strain gauges in each rotor blade are electrically connected to the controller which control an actuator connected to each of the flaps. The electrical cables extending from the rotor blade to the nacelle twist during the pitching which may cause the insulation on the electrical cables to break off resulting in a short circuiting. If the flap actuator is located in the rotor hub, the pneumatic/hydraulic hoses extending into the rotor blade also twist during pitching which may cause them to buckle or rupture resulting in a failure. This limits the pitching in one direction which means the rotor blade has to be pitched in the opposite direction when the maximum pitching angle is reached.
U.S. 2011/0076142 A1 corresponds to U.S. Pat. No. 8,360,723 B2 discloses a method of controlling a wind turbine in an idle situation in which each of the two or more rotor blades are pitched into different pitch angles. A controller continuously monitors the yawing capability and determines the pitch angle of each rotor blade based on measured vibration data and wind condition data. If grid power is not available, the rotor blades are positioned and maintained in an optimised position for various wind conditions. If grid power is available, the pitching of the rotor blades may be adjusted according to the wind direction so that the difference in pitch angle between the rotor blades is between 30 to 120 degrees. This method requires the rotor blades to be positioned in different positions so that the wind turbine experiences different loads on each rotor blades. The teachings suggest the use of strain gauges located on the rotor blade connected to the controller which requires the use of the electrical cables extending from the rotor blade to the nacelle. These electrical cables twist during the pitching which may cause the insulation on the electrical cables to break off resulting in a short circuiting.